White House national security adviser John Bolton departed on Saturday for a trip to Japan and South Korea as the two countries are in the middle of a trade dispute.

A White House National Security Council spokesman said on Twitter that Bolton planned to "continue conversations with critical allies and friends."

President Donald Trump on Friday offered his help to ease tensions in the political and economic dispute between the United States' two biggest allies in Asia, which threatens global supplies of memory chips and smartphones.

Lingering tensions, particularly over the issue of compensation for South Koreans forced to work for Japanese occupiers during World War Two, worsened this month when Japan restricted exports of high-tech materials to South Korea.

Japan has denied that the dispute over compensation is behind the export curbs, even though one of its ministers cited broken trust with Seoul over the labor dispute in announcing the restrictions.

The export curbs could hurt global technology companies.

Trump told reporters at the White House on Friday that South Korean President Moon Jae-in had asked him if he could get involved.

A spokeswoman for Moon confirmed Moon had asked Trump for help at their summit in Seoul on June 30.

During his trip, Bolton is also likely to seek support for a U.S. initiative to heighten surveillance of vital Middle East shipping lanes, which has been greeted warily by allies reluctant to raise tensions with Iran, which Washington blames for attacks on tankers.

Japanese media has said the issue could be on the agenda when Bolton visits Japan, where any military commitment abroad would risk inflaming a divide in public opinion in a country whose armed forces have not fought overseas since World War Two.

A South Korean official said last week Washington had yet to make any official request to Seoul on the issue.

The chairman of the U.S. Joint Chiefs of Staff, Marine General Joseph Dunford, said this month Washington hoped to enlist allies in a military coalition to safeguard strategic waters off Iran and Yemen, where Washington blames Iran and Iran-aligned fighters for attacks.

But with allies reluctant to commit new weaponry or fighting forces, a senior Pentagon official told Reuters on Thursday the aim was not to set up a military coalition but to shine a "flashlight" in the region to deter attacks on commercial shipping.

Kathryn Wheelbarger, who briefed NATO allies in the past week on the U.S. proposal, said it was less operational and more geared toward increasing surveillance capabilities.

Japan is the world's fourth-biggest oil buyer and 86% of its oil supplies last year passed through the Strait of Hormuz, a vital shipping route linking Middle East oil producers to markets in Asia, Europe, North America and beyond.

Japan's position is complicated by the fact that it has maintained friendly ties with Iran which it would be reluctant to damage. Japanese Prime Minister Shinzo Abe made an unsuccessful bid to ease tensions in the region when he met Iranian leaders in Tehran last month.